The present invention is directed to mechanism for suppressing an arcing condition across a brush-contact ring assembly in a vehicle horn-actuating circuit. By thus suppressing the arcing condition it is possible to suppress electromagnetic interference that would disturb or interfere with radio reception in the same vehicle or other vehicles in the immediate vicinity. The invention is partly concerned with the incorporation of a conventional capacitor into the horn circuit without changing, destroying, or modifying the existing electric components or their mounting mechanisms. The invention is especially intended as an add-on or retrofit device usable in a range of existing military vehicles without extensive cost to remove or replace components.